Some PCs show USB connection issues after being updated to Windows 8.1. Our research and the feedback from our customers shows that this is caused the forced USB power save functions of the lastest Windows update. Please check the following article to resolve the issue:http://support.microsoft.com/kb/2900614

On some other systems a similar issue is caused by the USB controller driver which is installed by Windows 8.1. If the solution explained in the MS KB article does not help we recommend to install the Windows 8(.1) driver from your mainboard/system vendor to resolve the issue.